Macrophage-restricted molecules: role in differentiation and activation.

Membrane antigens serve as excellent markers of murine macrophage (MO) differentiation in vivo and in vitro, and have yielded insights into novel MO functions in innate and acquired immunity. We review briefly the use of a range of monoclonal antibodies against MO which show restricted expression: F4/80, macrosialin and sialoadhesin. Differential display PCR strategies have made it possible to identify a novel MO-restricted membrane molecule, a murine MO C-type lectin (mMCL). The isolation of functionally active ab against known receptors such as the scavenger receptor, Class A (SR-A) has provided a key reagent to characterise the role of this molecule in adhesion, endocytosis, phagocytosis and in the regulation of cellular immunity. Studies in SR-A ko mice challenged with BCG and LPS show that the SR-A molecule helps to limit excessive production of cytokines such as TNFalpha by MO that have been activated by infection, and thus protects the host against septic shock.